Low-Pressure EGR Valve Timing Control for Combustion Stability
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Solution Overview
Problem
Low-pressure EGR systems experience combustion instability due to unnecessary inflow of external EGR gas when the system is stopped, leading to accidental fires and start-off phenomena, primarily because the recirculation pipe's length causes a delay in stopping exhaust gas inflow, especially at lower engine speeds.
Innovation Solution
An apparatus and method that include a driving information detector, an EGR amount detector, and a controller to adjust the timings of intake and exhaust valves, reducing valve overlap by retarding the intake valve and advancing the exhaust valve to decrease the internal EGR amount when the external EGR is decreased, thereby minimizing the unnecessary inflow of external EGR gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the low-pressure EGR valve is controlled to stop external EGR inflow, then the EGR rate is reduced to 0%, but exhaust gas continues to be introduced into the cylinder by inertia due to the long recirculation pipe, causing combustion instability
Solution Approach 1:
The controller predicts the residual EGR inflow based on the current EGR rate and engine speed, and proactively adjusts the intake valve timing in advance to compensate for the inertial flow that will occur after the EGR valve closes. This preliminary adjustment prevents combustion instability before it occurs.
Solution Approach 2:
The system continuously monitors the actual EGR inflow and compares it with the target EGR rate, then adjusts the intake valve timing accordingly. This feedback mechanism ensures that the intake valve timing is optimized to counteract the inertial effect of the recirculation pipe, maintaining combustion stability during EGR transitions.
2Reliability
If the intake valve timing is adjusted to compensate for inertial EGR inflow, then combustion stability is improved, but the valve timing control complexity increases
Solution Approach 1:
The controller calculates the optimal intake valve timing adjustment based on measurable parameters such as engine speed and current EGR rate. By using these existing operational parameters to determine the compensation timing, the system avoids adding complex sensing or mechanical components while still achieving stable combustion during EGR transitions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces combustion instability and prevents start-off phenomena by accurately controlling the valve timings to match the desired EGR rate, ensuring stable engine operation even when the low-pressure EGR system is stopped.
Implementation Method 1
the exhaust gas within the recirculation pipe is introduced, as it is, into a cylinder by inertia
Data Source
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AI summary
An apparatus for controlling a low-pressure EGR system may include a driving information detector configured to detect a vehicle driving state, an EGR amount detector configured to detect an amount of external EGR controlled by a low-pressure EGR valve, and a controller configured to control the low-pressure EGR valve and intake and exhaust valves of an engine, based on the result detected by the driving information detector and the EGR amount detector, wherein the controller controls timings of the intake and exhaust valves to decrease an amount of internal EGR introduced into a cylinder through an exhaust port for a predetermined time when the amount of external EGR is decreased.